Because of the discharge of salt brine into the environment from water softening systems, sensing of the time for regeneration in such systems has become of increased importance and improved sensors can contribute to improved conditions in the environment. Heretofore, sensors have been provided which sense a difference in conductivity of a resin in a calcium state and such resin in a sodium state, but this type of device requires comparison of changing resistances as distinguished from the system utilized herein, where the sensor senses the difference between a dead short and the conductivity of the water between a contact member and a circuit completing member. Since the conductivity of water is very high it becomes quite simple in this system to sense a dead short electronically versus any resistance and this simplifies the electronic circuitry utilized in this improved sensor as compared to previous designs.
Certain prior art sensing devices have been embedded in the exchange material of softener systems but these devices have been enclosed and therefore were not fully sensitive to changing conditions in the material and were slow to respond to such changes. Examples of sensing devices of this type can be found in U.S. Pat. Nos. 3,477,576, 3,512,634 and 3,250,392 wherein a strip of ion exchange ribbon was placed inside a plastic tube and as a consequence the ribbon was very sluggish in responding to changing conditions of the water because it was not in direct contact with the ion exchange material in the treatment tank and because the ribbon was enclosed contact with the flow of water was not readily made. Because of the enclosed type construction filter screens were incorporated which became clogged and further delayed response time of the sensing element because of the restricted flow of water through the screens. Further, the screens regardless of whether they were clogged or clean, necessitated greater hydraulic pressure to force the water through the screens to come in contact with the ion exchange ribbon. Also, because of the very nature of the construction utilized in these sensing devices they are more complicated and require additional space.